1. Field of the Invention
The present invention relates to a liquid crystal display monitor, a source driver and a control method thereof, and more particularly, to a liquid crystal display monitor, a source driver and a control method thereof capable of timely switching a driving method by detecting a common electrode voltage.
2. Description of the Prior Art
Since liquid crystal display monitors (LCD monitors) have the advantages of lightweight, low power consumption and free of radiation emission, they have been widely used in information products such as computer systems, mobile phones and personal digital assistants (PDAs). The operating principle of the LCD monitors is based on the effect that different arrangements of liquid crystal molecules result indifferent levels of polarization or refraction of light. Therefore, the amount of light penetration can be controlled by different arrangements of liquid crystal molecules, so as to generate output light with different intensities and different gray-levels of red, green and blue light. A timing controller is generally utilized in an LCD monitor for generating a data signal related to a displayed image and a control signal and a clock signal needed for driving the LCD panel. A source driver of the LCD monitor then generates a driving signal of the LCD panel according to the data signal, the control signal and the clock signal.
In general, a polarity of a voltage signal applied to a liquid crystal material layer needs to be inverted from time to time, to prevent the liquid crystal material from being polarized which leads to permanent damage and prevent from image sticking effect. Generally, methods such as frame inversion, line inversion or dot inversion are used for driving the LCD monitor, and therefore, the source driver needs to repetitively perform charging and discharging so as to provide the driving signal with different polarities. On the other hand, the output of the timing controller may also be switched between logic 1 and logic 0.
During operation, the LCD monitor may generate a common electrode voltage (Vcom), which is related to crosstalk. Crosstalk is a phenomenon by which a certain area of the image affects brightness of a neighboring area in an LCD panel. One of the reasons for crosstalk is poor stability of the common electrode voltage. For an LCD monitor used in a television, the LCD panel mainly displays motion pictures, for which crosstalk is not easy to occur. Hence, most of LCD monitors used in televisions nowadays are not designed with crosstalk elimination. However, for LCD monitors used in smart televisions, the LCD monitors may display more static pictures, and therefore, chances of having crosstalk are significantly increased.
Two methods are mainly applied for solving the crosstalk problem for LCD monitors, one of which is to stabilize the common electrode voltage. However, for LCD monitors with large size, a load of the common electrode voltage is high, such that a feedback compensation control over the common electrode voltage is difficult to be performed.
The other method to solve the crosstalk problem is to change the driving method of the timing controller by special patterns. In the industry, a conventional LCD monitor is capable of switching the driving method by detecting special patterns in the display frame, so as to prevent crosstalk.
Please refer to FIG. 1, which is a schematic diagram of a conventional LCD monitor 10. The LCD monitor 10 includes an LCD panel 100, a timing controller 102 and a driving circuit 104. The LCD panel 100 is used for displaying a frame, composed of two substrates, where an LCD layer is filled in between. The timing controller 102 is used for generating a data signal related to the displayed image and a control signal and a clock signal, i.e. a polarity control signal POL and a latch signal LD, required for driving the LCD panel 100. The timing controller 102 further detects special patterns in the displaying frame of the LCD panel 100. After detecting a special pattern, the timing controller 102 transmits a horizontal dot inversion control signal H2DOT, and changes the driving method of the LCD panel 100 to a horizontal two-dot inversion driving method. The driving circuit 104 includes a plurality of source drivers SD_1-SD_i, which generate respective driving signals in response to signals transmitted from the timing controller 102, for changing the arrangement and the corresponding amount of light penetration of the liquid crystal molecules in the LCD panel 100, to display image data on the LCD panel 100.
Please continue referring FIG. 2, which is a schematic diagram of a conventional source driver 20. The source driver 20, representing the source drivers SD_1-SD_i in FIG. 1, includes a horizontal dot inversion control unit 200 and an output unit 202. When the horizontal dot inversion control unit 200 detects the special patterns in the frame, it generates a horizontal dot inversion control signal H2DOT, so as to switch the driving method of the output unit 202 to the horizontal two-dot inversion driving method. The output unit 202 is coupled to the horizontal dot inversion control unit 200, for adjusting the driving method thereof according to the horizontal dot inversion control signal H2DOT, the polarity control signal POL and latch signal LD.
The conventional LCD monitor 10 is capable of detecting various special patterns and determining whether crosstalk occurs. For example, please refer to FIG. 3A, which is a schematic diagram of a special pattern 300A in a frame 30A. The special pattern 300A is composed of eight bright sub-pixels and seven dark sub-pixels, which are interlacedly arranged. That is, each two bright sub-pixels are with a dark sub-pixel located in between. If the timing controller 102 detects that the special pattern 300A exists in the frame 30A, the timing controller 102 generates horizontal dot inversion control signal H2DOT in order to switch the driving method to the horizontal two-dot inversion driving method. On the other hand, the above-mentioned eight bright sub-pixels and seven dark sub-pixels may be interspersed in a same frame. As shown in FIG. 3B, the special pattern 300B includes eight bright sub-pixels and seven dark sub-pixels interspersed in a frame 30B. Similarly, if the timing controller 102 detects that the special patterns 300B exists in the frame 30B, the timing controller 102 generates the horizontal dot inversion control signal H2DOT in order to switch the driving method to the horizontal two-dot inversion driving method.
However, for large-size LCD monitors, it is hard to design the special patterns for detecting crosstalk in the frame due to larger areas of displaying frame. Take FIG. 3B as an example. If the bright sub-pixels and the dark sub-pixels are separated with each other for a long distance, the timing controller needs to scan through almost the entire frame to detect the special patterns. Thus, it is not easy to detect the special patterns, resulting in a probably decrease of the screen display quality.